My Clinical Notes
- Consists of two lateral lobes connected by an isthmus
- Located below and anterior to the larynx
- Weighs 15-25g
- Supplied by the superior and inferior thyroidal arteries
- Nervous supply comes from the cervical sympathetic ganglia which influence thyroid function by controlling the blood supply
- Divided into lobules which are composed of 20-40 follicules
- Thyrotropin releasing hormone (TRH) is released from the hypothalamus which stimulates the anterior pituitary to release TSH. TSH stimulates release of thyroxina (T4) and lesser amounts of triiodothyronine (T3)
- Most binds to serum proteins such as thyroxine binding globulin (TBG)
- In the periphery the majority of T4 is deionated to T3 which has a ten times greater affinity for the thyroid hormone nuclear receptors
- Thyroid hormone acts to increase the basal metabolic rate. It is also important in brain development during fetal and neonatal periods
- Thyroid gland increases in size and becomes more active during pregnancy, puberty and physiological stress
- The antithyroid agent, propylthiouracil inhibits the oxidation iodide and blocks the production of thyroid hormones. In the periphery it blocks the deionation of T4 into T3
- Iodide when given in large amounts blocks the release of thyroid hormones by inhibiting the proteolysis of thyroglobulin. Therefore the thyroid hormone accumulates but is not release
- The thyroid gland also contains a population of cells called parafollicular or C cells which produce calcitonin. Calcitonin promotes absorption of calcium by the skeletal system and inhibits osteoclast function
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